The vinca alkaloids constitute a family of indole-indoline dimeric natural product compounds that continue to have a remarkable impact on anticancer drug discovery and treatment [Neuss et al., In The Alkaloids; Brossi, A., Suffness, M., Eds.; Academic: San Diego, Calif., 1990; Vol. 37, pp 229-240; Pearce, In The Alkaloids; Brossi, A., Suffness, M., Eds.; Academic: San Diego, Calif., 1990; Vol. 37, pp 145-204; and Kuehne et al., In The Alkaloids; Brossi, A., Suffness, M., Eds.; Academic: San Diego, Calif., 1990; Vol. 37, pp 77-132]. Originally isolated as trace constituents of the Madagascar periwinkle plant (Catharanthus roseus (L.) G.Don) [Noble et al., Ann. N.Y. Acad. Sci. 1958, 76, 882-894; and Svoboda et al., J. Am. Pharm. Assoc. Sci. Ed. 1959, 48:659-666], are a family of indole-indoline dimeric compounds that contain a four-ring system containing an indole linked to a five-ring system containing an indoline. Two of those natural alkaloid compounds, vinblastine (1) and vincristine (1a), are important clinical agents in the treatment of leukemias, lymphomas and testicular cancer. The semi-synthetic vinca alkaloid compound, vindesine (1b) is used to treat lung cancer and acute leukemia and less often for melanoma, and breast cancer. [Goodman & Gilman's The Pharmaceutical Basis of Therapeutics, Hardman et al. Eds., 9th ed., McGraw-Hill, 1257-1260, 1996.]
 R1R2R3Vinblastine (1)—CH3 Vincristine (1a) Vindesine (1b)—CH3—OH
The 19,20′-anhydrovinca alkaloids (anhydrovinca alkaloids) are also active in treating the above diseases, albeit, they are usually somewhat less potently cytotoxic. Thus, the semi-synthetic anhydrovinca alkaloid, vinorelbine, has activity against lung cancer and breast cancer, and anhydrovinblastine is active as is shown hereinafter. Anhydrovincristine and anhydrovindesine are also cytotoxic.
Of the above compounds, vinblastine (1) and vincristine (1a) are the most prominent members of this class, and are among the first plant-derived natural products used in the clinic for the treatment of cancer. These two compounds and three recent semi-synthetic analogs are integral oncology drugs employed today in highly successful combination drug successful combination drug therapies. Their mode of action, which involves disruption of tubulin assembly during mitosis, still remains one of the most successful approaches for inhibiting tumor cell growth [Jordan et al., Nat. Rev. Cancer 2004, 4:253-265].
Alterations to the target tubulin could also impact activity and contribute to or be responsible for vinca alkaloid resistance. A series of association studies of clinical data have implicated high level expression of class III β-tubulin as both a prognostic and predictive factor for lower response rates or reduced overall survival in patients receiving tubulin binding drugs [Seve et al., Lancet Oncol. 2008; 9:168 and Yang et al., PLoS One 2014; 9:e93997]. However, most of the association studies and the supporting cellular studies have examined the impact of class III β-tubulin on taxanes and a much smaller sampling of its impact on vinca alkaloids are represented in the association studies [Sève et al., Lancet Oncol. 2008; 9:168 and Yang et al., PLoS One 2014; 9:e93997].
Despite the obvious differences in the tubulin binding sites of the taxanes and vinca alkaloids as well as their distinct functional behaviors (stabilization vs destabilization of tubulin dynamics), both taxanes and the vinca alkaloids typically have been lumped together as potentially being negatively impacted by the high expression of class III β-tubulin [Sève et al., Lancet Oncol. 2008; 9:168 and Yang et al., PLoS One 2014; 9:e93997].
Vinblastine and vincristine are superb drugs even by today's standards. The major limitation to their continued use is the observation of clinical resistance mediated by overexpression of the drug efflux pump phosphoglycoprotein (Pgp) [Persidis, Nat. Biotechnology 1999, 17:94-95]. The identification of vinca analogs that might address such resistance, which also results in multidrug resistance (MDR) and is responsible for the majority of all relapses in oncology, has remained a major focus of the field for over 30 years.
Not only would the discovery of a vinca alkaloid such as an illustrated vinblastine analog not susceptible to Pgp efflux serve as an effective replacement for vinblastine in its current clinical uses or in instances of vinblastine resistance, but it could also emerge as a new therapeutic option for other Pgp-derived MDR tumor treatments and constitute a major advance for oncology therapeutics. Thus, Harmsen et al., Cancer Chemother Pharmacol 2010 66:765-771, teach that each of vincristine, tamoxifen, vinblastine, docetaxel, cyclophosphamide, Xutamide, ifosfamide and paclitaxel activate PXR-mediated Pgp induction. As a consequence, a contemplated Pgp efflux-insensitive vinca 20′ alkaloid amide can be used in place of one or more of those medicaments to inhibit PXR-mediated Pgp induction, while providing a desired anti-cancer therapy.
Despite the efforts focused on vinblastine for the past 40 years that have searched for analogs that effectively overcome vinblastine resistance, little progress has been made [Pearce, In The Alkaloids; Brossi, A., Suffness, M., Eds.; Academic: San Diego, Calif., 1990; Vol. 37, pp 145-20]. Recent advances in the total synthesis of vinblastine, vincristine and related natural products have provided access to analogs of the natural products not previously accessible by semisynthetic modification of the natural products [Potier, J. Nat. Prod. 1980, 43:72-86; Kutney, Acc. Chem. Res. 1993, 26:559-566; Sears et al., Acc. Chem. Res. 2015, 48:653-662; Fahy, Curr. Pharm. Des. 2001, 7:1181-1197; Langlois et al., J. Am. Chem. Soc. 1976, 98:7017-7024; Kutney et al., Helv. Chim. Acta 1976, 59:2858-2882; Kuehne et al., J. Org. Chem. 1991, 56:513-528; Bornmann et al., J. Org. Chem. 1992, 57:1752-1760; Yokoshima et al., J. Am. Chem. Soc. 2002, 124:2137-2139; Kuboyama et al., Proc. Natl. Acad. Sci. U.S.A. 2004, 101:11966-11970; Magnus et al., J. Am. Chem. Soc. 1990, 112:8210-8212; and Ishikawa et al., J. Am. Chem. Soc. 2009, 131:4904-4916].
The latest of these efforts has provided a powerful approach to access a variety of vinca alkaloid compounds, particularly vinblastine analogs that contain systematic deep-seated modifications within either the lower vindoline-derived [Ishikawa et al., J. Am. Chem. Soc. 2006, 128:10596-10612; Choi et al., Org. Lett. 2005, 7:4539-4542; Yuan et al., Org. Lett. 2005, 7:741-744; Elliott et al., Angew. Chem., Int. Ed. 2006, 45:620-622; Ishikawa et al., Heterocycles 2007, 72:95-102; Sears et al., Org. Lett. 2015, 17:5460-5463; Wilkie et al., J. Am. Chem. Soc. 2002, 124:11292-11294; and Elliott et al., J. Am. Chem. Soc. 2006, 128:10589-10595] or upper catharanthine-derived [Fahy, Curr. Pharm. Des. 2001, 7:1181-1197] subunits [Vukovic et al., Tetrahedron 1988, 44:325-331; Ishikawa et al., J. Am. Chem. Soc. 2008, 130:420-421; and Gotoh et al., J. Am. Chem. Soc. 2012, 134:13240-13243].
IC50, nMcompoundHCT116HCT116/VM461, X = OH6.86004, X = H606005, X = N369055006, X = NH2600>10000
As a result of these developments, the inventor and his research group have prepared several series of key analogs, systematically exploring and defining the impact individual structural features and substituents have on tubulin binding affinity and tumor cell growth inhibition [Sears et al., Acc. Chem. Res. 2015, 48:653-662; and Ishikawa et al., J. Am. Chem. Soc. 2009, 131:4904-4916]. Complementary to the studies detailed herein, the impact and role of the vindoline C4 acetate [Campbell et al., Org. Lett. 2013, 15:5306-5309; and Yang et al., Chem. Sci. 2017, 8:1560-1569], C5 ethyl substituent [Va et al., J. Am. Chem. Soc. 2010, 132:8489-8495], C6-C7 double bond [Sasaki et al., J. Am. Chem. Soc. 2010, 132:13533-13544; Kato et al., J. Am. Chem. Soc. 2010, 132:3685-3687; and Schleicher et al., J. Med. Chem. 2013, 56:483-495], and the vindoline core structure itself [Schleicher et al., J. Med. Chem. 2013, 56:483-495], and have systematically explored the upper catharanthine-derived subunit C20′ ethyl substituent [Allemann et al., J. Am. Chem. Soc. 2016, 138:8376-8379; and Allemann et al., Bioorg. Med. Chem. Lett. 2017, 27:3055-3059], C16′ methyl ester [Tam et al., Bioorg. Med. Chem. Lett. 2010, 20:6408-6410], and added C10′ or C12′ indole substitutions have been systematically probed Gotoh et al., ACS Med. Chem. Lett. 2011, 2:948-952].
In addition and in preceding studies, it has been shown that replacement of the C20′-OH with 20′ ureas was possible [Leggans et al., Org. Lett. 2012, 14:1428-1431], that substantial [Leggans et al., J. Med. Chem. 2013, 56:628-639] and even remarkable [Carney et al., Proc. Natl. Acad. Sci. U.S.A. 2016, 113:9691-9698] potency enhancements were obtainable with such 20′ ureas, and that some exhibited further improvements in activity against vinblastine-resistant tumor cell lines [Barker et al., ACS Med. Chem. Lett. 2013, 4:985-988].
Looking across the vinca alkaloid compounds, is seen that similarities in activity on substitution with the same group at the same position of different vinca alkaloids, and particularly among these three particular alkaloid compounds (1, 1a, and 1b), provide similar results in anti-cancer cell activity increase or decrease. These activity similarities on substitution provide a predictive result across the group of at least the three vinca alkaloids that are vinblastine (1), vincristine (1a) and vindesine (1b).
 R1R2R3Vinblastine (1)—CH3 Vincristine (1a) Vindesine (1b)—CH3—OH
See, for example, Gotoh et al., ACS Med Chem Lett 2011 2:948-952 and U.S. Pat. No. 8,940,754, where vincristine and vinblastine that had almost identical activities against two cancer call lines and a MDR variety of one of those lines on substitution of each of vincristine and vinblastine at the 10′-position with a fluoro group, provided fluoro-derivative compounds with enhanced, and almost identical activities in those same cancer cell lines. See also, U.S. Pat. No. 7,238,704 where activities among identically substituted vinblastines, vincristines, anhydrovinblastines, anhydro-vincristines are illustrated and are seen to be similar. Those activities can also be seen to be comparable to the activities of identically substituted vinorelbines that are illustrated in U.S. Pat. No. 7,235,564.
An important extension of these studies is disclosed herein that includes the evaluation of vinblastine 20′ amides with a prescribed objective of discovering analogs that match or exceed the potency of vinblastine, but that are not subject to Pgp efflux and its derived vinblastine resistance. Not only did these studies provide vinblastine analogs no longer susceptible to Pgp-derived resistance, but those compounds illustrate the discovery of a site and functionalization strategy for the preparation of now readily accessible vinca alkaloid analogs (3 steps) that improve binding affinity to tubulin (on target affinity) and functional potency in cell-based assays while simultaneously disrupting efflux by Pgp (off target affinity and source of resistance), offering a uniquely powerful approach to discover new, improved, and durable oncology drugs.